Sheet metal that is subjected to a metal stamping process often will springback toward its original shape such that angles formed in the stamped part will be larger than those of the corresponding stamping tool. Springback can result in angular changes of the side wall, side wall curl, or twist or torsion springback. It is desirable to reduce such springback to improve dimensional and shape quality and consistency in the stamped parts.
Traditionally, side wall curl spring back is controlled using a post-forming stretching operation. For example, stake beads are typically used to engage a flanged portion of the part to apply a post-stretch or tension to side walls of the part. The deformations caused by the stake beads are subsequently removed and discarded.
Such post-stretching processes to control springback require an additional width of wasted flange material on all sides of the part. The waste material and the additional process steps and equipment required to remove and discard the waste material add costs and reduce operational efficiency and throughput. In addition, the stake bead forming die elements tend to wear prematurely relative to the other die elements.
In addition, many sheet metal materials, including high strength aluminum and high strength steel, tend to exhibit relatively poor formability or ductility. In other words, such material will tend to exhibit cracking when subjected to relatively small amounts of stretching and bending. For such materials, the use of post-stretching process requires additional formability, ductility, or stretchability beyond that required to form the part, which serves to further limit the shapes of parts that these materials can form.